1. Field of the Invention
This invention relates to a power system for a computer, and more particularly, to a power system for a computer which automatically selects the voltage to the computer system and also the frequency of operation of the computer system based on the current requirements of the system or upon a control signal from the computer system.
2. Description of the Prior Art
Present day portable computers have limitations on the length of time they operate before exhausting the batteries in the system. Typical portable computers heretofore known operate at a single voltage, typically 5 volts, and utilize system clocks having a fixed frequency. There are certain disadvantages to this in that they do not incorporate features to reduce the load on the batteries and therefore extend their life. In a typical integrated circuit device utilizing CMOS semiconductor devices, the power consumed by the system is expressed by the equation EQU P=CV.sup.2 F.
Since the capacitance of a system is a variable not available for adjustment by designers, the possible variables which could be changed are the system voltage and the operating frequency. Prior art computer systems are known which include clocks having more than one frequency, however the variable frequency clocks were utilized as a function of the mode of operation and not responsive to the average usage over a period of time. In the prior art systems if the power supply was unable to provide the required voltage for a high frequency clock operation, the system would lose data because the clock could not operate at a frequency less than its maximum and was not tailored to permit operation at a lower supply voltage if that was all that was available. Also in the prior art systems there was not the ability to provide a continuing voltage and system clock frequency relationship in which the system clock varied over a continuum of possible supply voltages.